Method and system for international roaming and call bridging

ABSTRACT

Disclosed is an enhanced system and method for bridging calls across telecommunications networks, including an illustrative application of the invention as it relates to international roaming among prepaid wireless subscribers. For instance, whenever wireless subscribers roam internationally they may invoke the system by keying in an Unstructured Supplementary Service Data (USSD) short code followed by the number to be dialed. Said subscriber&#39;s prepaid account is then decremented in real-time (until such account is fully depleted). A key feature of the disclosure generally is the bridging of the call legs between the wireless subscriber initiating the telephone communication and that of the receiving party through a series of general purpose databases and computers without requiring modifications to existing core network or handset infrastructure

BACKGROUND ART

International roaming and more generically, the bridging of calls acrosstelecommunications networks is well detailed in the prior art literaturerelated and industry know-how. For instance, U.S. Patent ApplicationPub. No. 2002/0061745 by Ahn et al., entitled Roaming Service System forGSM Service Subscriber in CDMA Service Area, and Method for RegisteringLocations and Transmitting and Receiving Signals and Short Messagesusing the System, calls for the installation of a GSM-type SIM card intothe CDMA terminal; our invention of present however remains independentof any such subscriber modification and/or registration.

Similarly, U.S. Pat. No. 6,075,855 to Christiansen et al., entitledMethod of Accessing a SCP in an ISUP Network with Partial Releasedetails art relevant to call set-up and clearing for intermediate accessto a SCP in an ISUP network. Nevertheless, the art disclosed thereinremains tied to the loop-back (‘hairpin’) trunk technique; a highlyundesirable technique given today's telecommunications infrastructure,as it redundantly ties up trunks and related network resources. Indeedthe art of the present invention remains independent of any such loopingand goes beyond much of the obviousness of that disclosed art. Otherrelated technology, as U.S. Pat. No. 6,393,289 to Bunting et al.,entitled Apparatus, Method and System for Wireless TelecommunicationSession Control by an Adjunct Network Entity, revolves around theinterpretation of an ANSI-41 command by an network adjunct. Under thatdisclosure, the network adjunct will in turn allow the call to proceed,hair-pin the call, or invoke other ANSI-41 directives in order toinstruct the switch to route the call without hair-pining the callthrough the network adjunct.

REFERENCES CITED

U.S. Patent Application Publication No. 2002/0061745 (May 2002) to Ahnet al.; U.S. Pat. No. 6,393,289 (May 2002) to Bunting et al.; U.S. Pat.No. 6,075,855 (June 2000) to Christiansen et al.

Other References

GSM 03.90, Digital cellular telecommunications system (Phase 2+);Unstructured Supplementary Service Data (USSD)-Stage 2

GSM 09.02, Mobile Application Part (MAP) specification

3GPP2 N.S0023, Network Support for MDN-Based Message Centers

TIA TR 45.2, IS-841, TIA/EIA-41-D Based Network Enhancements for MDNBased Message Centers

TIA/EIA ANSI-41 Cellular Radiotelecommunications Intersystem Operations

TECHNICAL FIELD

The present invention relates generally to wireless communications andservices; and more specifically, to an improved method and system forthe bridging of calls across telecommunications networks.

SUMMARY OF THE INVENTION

Particular attributes of traditional Intelligent Network (IN)environments have inherently constrained the development and geographicscope of applications which utilize the capabilities of today'snetworks. The asynchronous development cycles of traditional INinfrastructure vendors have led to variants in vendors' implementationsof IN technologies. This point, as well as the inclusion of proprietaryextensions to IN signalling protocols, have made interworking of INservices an ongoing issue faced by wireless carrier—particularly whereinterworking between a mix of vendor platforms is required. Theselimitations have effectively precluded the geographic scope of popularwireless ‘prepaid’ services to areas within the operating region of agiven carrier where the carrier has deployed core network infrastructure(e.g. Home Location Registers (HLRs), Mobile Switching Centers (MSCs),Service Control Points (SCPs)) associated with a common vendor.

As such, the improved method and system for Call Bridging andInternational Roaming disclosed herein is an innovative networkapplication, enabling prepaid subscribers to place calls wheneverroaming out with their home network or in the invocation of otherapplications which involve bridging the subscriber to another subscriberor to a service provider.

Upon being initiated, the system sets up calls to both the originatingand destination party, and bridges them together. The call bridge is ineffect ‘forced’.

Specifically, the calls are bridged using the switching fabric of agiven Mobile Switching Center using the procedures and operationsassociated with the SS7 ISDN User Part (ISUP) protocols in an innovativemanner as disclosed herein. An illustrative aspect of the disclosed artalso permits mobile phone operators to log and transact calls made byprepaid subscribers when they are away from their homenetwork-effectively expanding the geographic scope of prepaid wirelessservices.

Although the method and system disclosed, by and large employs a seriesof general purpose databases, filters and computers to achieve its ends,the bona fide distinctiveness of the invention resides in the so-calledcall setup module (CSM), which principally incorporates much of thefunctional and operative aspects of the invention.

A subscriber may invoke the call-bridging procedures by initiating amessage to the CSM. A variety of mechanisms may be utilized by a givensubscriber for the purpose of sending a message. These messagingmechanisms may include, but are by no means bounded by, Short MessageService (SMS), Unstructured Supplementary Service Data (USSD), Internetbrowser, or a voice-based call using Dual-Tone-Multi-Frequency (DTMF)Interactive Voices Response based technologies. The message may berouted directly via existing telephony protocols or may be routedindirectly via a messaging gateway. The information provided via themessaging mechanism will typically include the identity of theoriginating subscriber, the destination address, and the service to beactivated.

The messaging gateway will also typically initiate the Call Bridgingprocedure via an Application Programming Interface (API) which willinclude a number of parameters including but not limited to theoriginating subscriber address, terminating subscriber address, and atransaction identifier. The purpose of the transaction identifier beingto uniquely correlate a given request with other messages which may bereceived asynchronously including, but not limited to, a confirmationresponse. Practitioners skilled in the art shall recognize that avariety of object oriented application programming interfaces (e.g.Common Object Request Broker Architecture (CORBA), Extensible MarkupLanguage (XML)) will serve the purpose of notification without affectingthe intent and scope of the present invention.

The CSM may also autonomously initiate the call-bridging procedure via arequest initiated by programmatic instructions stored in an softwareapplication resident in the CSM. For example, the CSM may invoke thecall-bridging procedure at a given prescribed time in order to bridge asubscriber to a recording for a wake-up service stored in the CSM.

The CSM performs a syntax and validity check to determine if the requestas received is well formed. It may also retrieve the subscriber'slocation in the Home Location Register (HLR) to assist the billingsystem in correctly rating the call. Additionally, the CSM is alsoresponsible for normalizing the called number and for event logging.

Indeed, the CSM requests the initiation of two call attempts first tothe subscriber (originating Mobile Station Integrated Services DigitalNetwork Number (MSISDN)) and, on successful establishment, subsequentlyto the requested ‘destination’. The call legs are each routed to adefined circuit of the ISUP loop around configured in the network bydefining the CIC for the call legs as equivalent.

The Bridging method, and its non-limited illustrative application toInternational Roaming, specifically utilizes a Loop Around mechanism inorder to leverage the inherent resilient switching fabric of the NetworkOperator's MSC. In a standard configuration a loop around facility isconfigured with an adequate number of circuits in order to accommodatethe anticipated traffic requirements associated with the method. The MSCis configured to treat each end of the call as a trunk-group to avirtual MSC associated with a given SS7 point code (that is, from theperspective of the MSC, the loop-around facility is treated as twotrunk-groups which terminate at another MSC).

The method will initially establish a call towards the originatingmobile pre-paid subscriber utilizing the attributes (CircuitIdentification Code) associated with one end of the loop-aroundfacility. Note that from the perspective of the loop-around equippedMSC, the loop-around equipped MSC will appear to be receiving an ISUPcall from another MSC. The loop-around equipped MSC will utilize itsexisting translation tables in order to direct the call via theappropriate out-bound facility in order to establish an ISUP call to theoriginating pre-paid mobile subscriber. Note that all ISUP traffic (e.g.the ACM, ANM, REL, RLC messages) associated with end of the loop-aroundfacility which is used to establish a call to the originating subscriberwill be terminated by the CSM. When the originating mobile subscriberhas answered the phone, an ANM message will be received by the CSM. TheCSM will in turn initiate the second leg of the call to the destinationsubscriber located in the PSTN (Public Switched Telephone Network) viathe other end of the loop-around facility. The CSM will necessarilycorrelate the Circuit Identification Codes so that the same facility(time-slot) is utilized at each end of the loop-around trunk-group for agiven call. The loop-around equipped MSC will similarly utilize itsexisting translation tables in order to direct the call via theappropriate out-bound facility to the destination subscriber via thePSTN. When the terminating PSTN subscriber has answered the phone, anANM message will be received by the CSM. At this point in time, theloop-around equipped MSC will effectively bridge the calls together viathe switching fabric of the loop-around equipped MSC and the correlatedtime-slot/facility of the loop-around trunk-group.

Should the destination number be otherwise busy, an audible busy signalfrom the receiver will be connected to the call originator. Thisconnection will be kept shortly, and then released. A message shall thenbe delivered to the call originator in this case, indicating thedestination number is busy. The message may be delivered via severalmechanisms, including but not limited to, SMS, USSD, and Simple MailTransfer Protocol (SMTP) based technologies.

Once the CSM detects a disconnection from either party by receiving anISUP REL message, the CSM will complete the release sequence on that legof the call as well as initiate a release sequence on the correlatedfacility on the other side of the loop-around trunk-group in order torelease the circuit-switched facilities towards the other party. Notethat if the release signal is initiated from the terminating PSTNsubscriber, the CSM may optionally initiate an ISUP call originationsequence via the loop-around facility in order to direct the originatingpre-paid subscriber to an IVR application for the purpose of receivingfurther instructions from the originating subscriber.

Indeed, these features and other such advantages of the presentinvention shall readily become apparent from the following descriptionand accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a configuration of the call bridging method andsystem in a sample telecommunications system in accordance with anon-limiting embodiment of the present invention;

FIG. 2 illustrates a typical, non-limiting embodiment of the systemlevel architecture employed in an exemplar articulation of the presentinvention involving call establishment procedures for prepaid mobilephones;

FIG. 3 details a non-limiting call-flow of a successful call set-up,illustrative of the bridging of the call legs in but one articulation ofthe present invention involving call establishment procedures forprepaid mobile phones.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference now to FIG. 1, which presents a configuration of theinvention in an exemplar telecommunications system. Members skilled inthe art will appreciate that the illustrated network elements do notrepresent all of the physical nodes used to realize a public mobiletelecommunications network. Indeed, those members shall also recognizethat additional transport and signalling facilities may be utilized inorder to establish connectivity among the network elements as generallydescribed in standards and specifications including, but not limited to,ANSI-41 and GSM 9.02. Detailed depictions of well known architecturesand network configurations are omitted so as not to obscure the art ofthe present invention with superfluous detail.

Again referring to FIG. 1, the SS7 12 network provides signallingconnectivity among a number of network elements in the public networkincluding Service Centers 13. Signalling connectivity via signallinginterfaces and transport mechanisms 11 can also be provided by otherprotocols including the Stream Control Transmission Protocol (STCP) andSession Initiation Protocol (SIP) specified by the Internet EngineeringTask Force (IETF). The Switching Center 13 provides for a source andsink of communications traffic as the Switching Center 13 servessubscribers (not shown) via land-line and mobile stations (not shown).The Switching Center 13 serves mobile stations (not shown) via basestations (not shown) and radio links (not shown). The connectivitybetween the mobile station and a given destination point such as anothermobile station (not shown) or another fixed station (not shown) isprovided via the Switching Center 13 which in turn provides SS7connectivity and transport connectivity via the Public or PrivateNetwork 15 via bearer transport mechanisms (e.g. E1 or T1 basedtransport facilities) 14 24. The Switching Center 13 also serves totandem traffic received from Public or Private Network 15 to anotherdestination point (not shown) in the Public or Private Network 15 aswell as alternative Switching Centers (not shown) or adjunct devices(not shown) which are directly interconnected with the Switching Center13. The Call Bridging Server 10 has direct or indirect connectivity tothe network elements of the telecommunications network including, butnot limited to, the Switching Center 13 using industry standardprotocols such as SS7 or SCTP.

Still in consideration of FIG. 1, the Switching Center 13 is equippedwith a loop-around transport facility 16. The loop-around transportfacility is a transport facility which provides connectivity between twoports 17 18 on the Switching Center 13. A given circuit or time-slot inthe loop-around transport facility 16 is terminated to the ports 17 18on the Switching Center 13. The circuit in the loop-around transportfacility 16 is correlated to two unique SS7 ISDN User Part CircuitIdentification Codes for the given Switching Center 13. Each port 17 18which is associated with a given end-point of the loop-around facilityis associated with a unique Circuit Identification Code. Those skilledin the art will recognize that several analogue or digital transmissionsystems may be used for the purpose of establishing the loop-aroundfacility including those based on E1 and T1 transmission standards.Details pertaining to the electromechanical nature as well as encodingmechanisms associated with well known transmission mechanisms areomitted so as not to obscure the description of the present inventionwith unnecessary detail.

Still in consideration of FIG. 1, the Call Bridging Server 10 willinitiate the call bridging procedure by initiating a call-set upprocedure to a destination point served by the Switching Center 13 or bythe Public or Private Network 15 via the switching fabric 21 andapplicable interface port 19 of the Switching Center 13. The destinationpoint may be a land-line or mobile station as well as a adjunct nodewhich provides a telecommunications service (for example an interactivevoice response based service). The Call Bridging Server will be equippedwith a unique SS7 identifier (signalling point code) and will appear tobe an adjacent adjunct to the Switching Center 10. Details associatedwith well known call establishment signalling mechanisms, operations,and procedures are omitted so as not to obscure the description of thepresent invention with unnecessary detail. The call-set up procedurewill utilize an Initial Address Message (LAM) which will include aCircuit Identification Code (CIC) associated with one end of the looparound transport facility which in turn is associated with one port 17on the Switching Center 13. The end of the loop around-facilityassociated with the initial call initiated by the Call Bridging serverwill be identified by a unique CIC for that Switching Center 13. Fromthe perspective of the loop-around equipped Switching Center 13, theSwitching Center 13 will appear to be receiving an LAM messageassociated with an incoming call from the Call Bridging Server 10. Theloop-around equipped Switching Center 13 will utilize its existingtranslation tables in order to direct the call via its internalswitching fabric 21 to the appropriate transport facility which mayinclude an outbound transport facility 14 to a destination point in thePublic or Private Network 15 or a termination point directly served bythe Switching Center 13 (for example, a mobile station served by a basestation). Subsequent call-establishment procedures involving the receiptand processing of SS7 call establishment messages associated with thecall initiated by the Call Bridging Server 10, including but not limitedto, the Address Complete Message (ACM) and the Answer Message (ANM) willbe directed to the Call Bridging Server 10 via the Switching Center 13and the SS7 Network 12. Each SS7 call establishment message associatedwith the call initiated by the Call Bridging Server 10 directed to theCall Bridging Server 10 will include the CIC associated with the circuitor time-slot of the loop around transport facility 16 which isterminated on the Switching Center 13 via a port 17. Subsequent to thedestination point answering the call initiated by the Call BridgingServer 10, an ANM message will be received by the Call Bridging Server10 message via the Switching Center 13 and SS7 Network 12. The CallBridging Server will in turn initiate the second leg of the call to asecond destination point served by the Switching Center 13 or by thePublic or Private Network 15 via the switching fabric 22 and applicableinterface port 20 of the Switching Center 13. The second destinationpoint may be a land-line or mobile station as well as a adjunct nodewhich provides a telecommunications service (for example an interactivevoice response based service). The call-set up procedure will utilize anLAM which will include a second Circuit Identification Code (CIC)associated with the other end of the loop around transport facilitywhich in turn is associated with a second port 18 on the SwitchingCenter 13. The Call Bridging Server 10 will correlate the CircuitIdentification Codes associated with the loop-around facility so thatthe same circuit (time-slot) is utilized at each end of the loop-aroundtrunk-group for a given call. From the perspective of the loop-aroundequipped Switching Center 13, the Switching Center 13 will appear to bereceiving an IAM message associated with a second incoming call from theCall Bridging Server 10. The loop-around equipped Switching Center 13will utilize its existing translation tables in order to direct thesecond call via its internal switching fabric 22 the appropriatetransport facility which may include an outbound transport facility 24to a destination point in the Public or Private Network 15 or atermination point directly served by the Switching Center 13 (forexample, a mobile station served by a base station). Subsequentcall-establishment procedures involving the receipt and processing ofSS7 call establishment messages associated with the call initiated bythe Call Bridging Server 10, including but not limited to, the ACM andthe ANM will be directed to the Call Bridging Server 10 via theSwitching Center 13 and the SS7 Network 12. Each SS7 call establishmentmessage associated with the second call initiated by the Call BridgingServer (10) will include the second CIC associated with the circuit ortime-slot of the loop around transport facility 16 which is terminatedon the Switching Center 13 via a port 18. Subsequent to successfulinitial contact with the second destination point, an ACM message willbe received by the Call Bridging Server 10 via the Switching Center 13and SS7 Network 12. The initial destination point may be able to hearcall progress tones (for example, ringing tone) at that point in time byvirtue of the connectivity established in the Switching Center 13 viathe connectivity established between two ports 19 20 via the switchingfabric 21 22 and the loop around transport facility 17 connected to theSwitching Center 13 via the facility termination ports 17 18. Subsequentto the second destination point answering the second call initiated bythe Call Bridging Server 10, an ANM message will be received by the CallBridging Server 10 message via the Switching Center 13 and SS7 Network12. The leg of the call to the first destination party will be bridgedto the leg of the call to the second destination party via the switchingfabric 21 22 of the Switching Center and the loop-around transportfacility 16. That is, the loop around transport facility 16 will bridgethe two destination parties utilizing the switching fabric 21 22 of theSwitching Center 13. The two parties may commence communications via theestablished bearer path which includes the two legs of the callinitiated by the Call Bridging Server 10 and the loop-around transportfacility. Subsequent to the release of a leg of the call via one of thedestination parties, a Release Message (REL) will be will be received bythe Call Bridging Server 10 message via the Switching Center 13 and SS7Network 12 for the leg of the call associated with the initiated callrelease. The received REL message will contain the CIC associated withthe leg and destination party which initiated call release. The CallBridging Server will initiate call-release procedures for the other legof the call by sending a REL message with a CIC associated with the portand leg of the call of the other destination party. Subsequent to thesuccessful release of the call, a Release Complete (RLC) message will bereceived by Call Bridging Server 10 message via the Switching Center 13and SS7 Network 12. The Call Bridging Server 10 will continuecall-release procedures by sending a RLC message with a CIC associatedwith the port and leg of the call of the destination party whichinitiated the call-release procedure. Those skilled in the art willrecognize that other SS7 messages may be initiated, propagated, andregenerated via the Switching Center 13 and Call Bridging Server withoutdiluting the material aspects of the invention. Those skilled in the artwill also recognize that the Call Bridging Server 10 may initiate thecall termination procedure on either leg of the call based onprogrammatic instructions for a particular telecommunications service.For example, if it is determined that the account for a giventelecommunications service has been depleted the Call Bridging Server 10may terminate the service by initiating call release procedures for bothlegs of the call. Those skilled in the art will also recognize that theCall Bridging Server 10 may elect not to propagate call releaseprocedures associated with one leg of a call and may initiate a callupon completing the call release procedures for a single leg of thecall. For example, upon completing the call release procedures for oneleg of the call, the Call Bridging Server 10 may initiate a call to asubsequent destination such as an Interactive Voice Response system forthe purpose of relaying information or receiving further instructionsfrom the subscriber connected to the loop around facility via theswitching fabric of the Switching Center and outbound transportfacility.

With reference to FIG. 2, whenever a prepaid wireless subscriber isroaming outwith his/her home network they may invoke the system bykeying in an Unstructured Supplementary Service Data (USSD) short code,*121* for instance, followed by the number to be dialed 201. The USSDmessage is automatically routed to the USSD Gateway 203 on the homenetwork via the Visitor Location Register (VLR)/Home Location Register(HLR) 202. The USSD message is routed to the USSD gateway using themethods, operations, and protocols specified in GSM 03.90 and GSM 09.02as amended from time to time. Details associated with well known messagedelivery methods and procedures are omitted so as not to obscure thedescription of the present invention with unnecessary detail. Thoseskilled in the art will recognize that a variety of alternativemechanisms may be utilized by a given subscriber for the purpose ofinvoking a service by sending a message. These mechanisms include, butare by no means bounded by, Short Message Service (SMS, Internetbrowser, or a voice-based calls using Dual-Tone-Multi-Frequency (DTMF)Interactive Voices Response based technologies.

Again with reference to FIG. 2, the call request is forwarded to thegeneral purpose Call Bridging Server (which houses the Call Setup Moduleand the International Roaming Application—a specific instance of theBridging application for illustrative purposes) 204. The request may bereceived via an Application Programming Interface (API) which willinclude a number of parameters including but not limited to theoriginating subscriber address, terminating subscriber address, and atransaction identifier. The purpose of the transaction identifier beingto uniquely correlate a given request with other messages which may bereceived asynchronously including, but not limited to, a confirmationresponse. Practitioners skilled in the art shall recognize that avariety of object oriented application programming interfaces (e.g.Common Object Request Broker Architecture (CORBA), Extensible MarkupLanguage (XML)) will serve the purpose of notification without affectingthe intent and scope of the present invention. Those skilled in the artshall also recognize that the request may be received by the CallBridging Server via telephony protocols as specified in GSM 03.90 andGSM 09.02 as amended from time to time. Details associated with wellknown message delivery methods and procedures are omitted so as not toobscure the description of the present invention with unnecessarydetail.

Still in consideration of FIG. 2, where the account balance (query 205)is greater than a predesignated threshold the International RoamingApplication (IRA) may initiate a Send Routing Information (SRI) messageto the HLR with a view to obtaining the Mobile Subscriber Roaming Number(MSRN) and VLR for the said roaming subscriber 206. Keeping with thisillustration, the (international roaming) bridging application alsoscreens service access; dictating for example, that only certain numbersmay be dialed, thereby preventing the very real and widespread concernamong wireless providers for abuse of service and other instances offraud.

Employing the subscriber/originator's MSISDN (or in alternateembodiments, the MSRN), the IRA formulates an ISUP Initial AddressMessage (LAM) message which is directed to the Mobile Switching Center(MSC) 207 via the SS7 network (not shown). The ISUP LAM message willcontain a Called Party Number parameter which is set to the MSISDN (orin alternate embodiments, the MSRN) and will contain the CIC associatedwith one end of the loop-around arrangement.

Still in consideration of FIG. 2, The MSC then proceeds to establish thecall to said roaming subscriber in Visited Mobile Switching Center(VMSC) 208 via the Public Switched Telephone Network (PSTN) (not shown).

The successful set-up of the first call leg triggers the InternationalRoaming Application to initiate set-up of second call leg (not shown).Initiating the second call over the corresponding circuit of the looparound circuit bridges the two calls together and the called party onthe first leg can hear the call progress (alerting) tones on the line).Said act thereof will further trigger to the Service Control Point (SCP)to verify sufficient balance 209, and initiates rating of the calls. Inalternate embodiments, prefix digits are prepended to the destinationnumber to aid the SCP in rating the call appropriately. In otheralternate embodiments, the RA may directly adjust the account balance ofthe SCP via an interface and protocol supported by the SCP.Correspondingly, when either the first of second leg hangs up, the otherleg of the call is also disconnected by the International RoamingApplication (the MSC would trigger the SCP to stop rating the call, anddeduct from the subscriber's account accordingly).

Now in reference to FIG. 3, at 101 the subscriber initiates a USSDrequest which is relayed to the USSD Gateway via the SS7 network. TheUSSD Gateway transfers the request to the International RoamingApplication (IRA); contained within which is the Call Control Module(CSM), which determines if said subscriber is within the designatedserving region, and in alternate embodiments, the status and nature ofthe subscriber's balance 102.

Now still in consideration of FIG. 3, The IRA will initially establish acall towards the originating mobile pre-paid subscriber utilizing theattributes (i.e. Circuit Identification Code) associated with one end ofthe loop-around facility. Note that from the perspective of theloop-around equipped MSC, the loop-around equipped MSC will appear to bereceiving an ISUP call from another MSC. The loop-around equipped MSCwill utilize its existing translation tables in order to direct the callvia the appropriate out-bound facility in order to establish an ISUPcall to the originating pre-paid mobile subscriber via the PSTN. Notethat all ISUP traffic (e.g. the ACM, ANM, REL, RLC messages) associatedwith the loop-around facility which is used to establish a call to theoriginating subscriber will be terminated by the CSM. The end of theloop around-facility associated the call established to the originatingpre-paid subscriber will be identified by a unique CIC for that MSC.When the originating mobile subscriber has answered the phone, an ANMmessage will be received by the CSM. The CSM will in turn initiate thesecond leg of the call to the destination subscriber located in thePublic Switched Telephone Network (PSTN) via the other end of theloop-around facility. The end of the loop around-facility associated thecall established to the destination subscriber will be identified by asecond unique CIC for that MSC.

The CSM will necessarily correlate the Circuit Identification Codesassociated with the loop-around facility so that the same facility(time-slot) is utilized at each end of the loop-around trunk-group for agiven call. The loop-around equipped MSC will similarly utilize itsexisting translation tables in order to direct the call via theappropriate out-bound facility to the destination subscriber via thePSTN. When the terminating PSTN subscriber has answered the phone, anANM message will be received by the CSM. At this point in time, theloop-around equipped MSC will effectively bridge the calls together viathe switching fabric of the loop-around equipped MSC and the correlatedtime-slot/facility of the loop-around transport facility 103.

The originating party will be able to hear the usual call progress tonesupon receipt of the second ACM at the loop-around equipped MSC. Theaccount associated with the originating subscriber (where prepaid) isdecremented using standard CAMEL/INAP messaging sequences on theso-called ‘PSTN’ side of the call. In alternate embodiments, thedestination number may optionally be prefixed to invoke a special chargein the SCP. In other alternate embodiments, the CSM may directly adjustthe subscriber balance via a protocol and interface supported by theSCP.

At 104, the call is connected.

While the foregoing describes what are considered to be the preferredembodiments of the invention, it is understood that variousmodifications may be made therein and that the invention may beimplemented in various forms and alternate embodiments, and indeed thatit may be applied in numerous applications, only some of which have beendescribed. The claims are intended to cover all such modifications andvariations which fall within the true scope of the invention.

1. A non-transitory computer readable medium storing computer readableinstructions executable by a processor of a call bridging server forimplementing a method comprising: receiving a request from a firstmobile station at the call bridging server, the request for initiating avoice call to a second mobile station; initiating a first call leg fromthe bridging server to the first mobile station; initiating a secondcall leg from the bridging server to the second mobile station; and,joining the first call leg with the second call leg at the bridgingserver to complete the voice call.
 2. The non-transitory computerreadable medium of claim 1 wherein the request is formed using ShortMessage Service (SMS).
 3. The non-transitory computer readable medium ofclaim 1 wherein the request is formed using Unstructured SupplementaryService Data (USSD).
 4. The non-transitory computer readable medium ofclaim 1 wherein the request is formed using a web browser.
 5. Thenon-transitory computer readable medium of claim 1 wherein the requestis formed using a voice-based call.
 6. The non-transitory computerreadable medium of claim 1, the method further comprising: determiningwhether an account balance associated with one of the first mobilestation and the subscriber is greater than a predesignated threshold. 7.A call bridging server, comprising: a communications interface; and aprocessor interconnected with the communications interface, theprocessor configured to: receive a request, via the communicationsinterface, from a first mobile station, the request for initiating avoice call to a second mobile station; initiate a first call leg to thefirst mobile station; initiate a second call leg to the second mobilestation; and, join the first call leg with the second call leg tocomplete the voice call.
 8. The call bridging server of claim 7 whereinthe request is formed using Short Message Service (SMS).
 9. The callbridging server of claim 7 wherein the request is formed usingUnstructured Supplementary Service Data (USSD).
 10. The call bridgingserver of claim 7 wherein the request is formed using a web browser. 11.The call bridging server of claim 7 wherein the request is formed usinga voice-based call.
 12. The call bridging server of claim 7, theprocessor further configured to: determine whether an account balanceassociated with one of the first mobile station and the subscriber isgreater than a predesignated threshold.